Glossary of Aquifer Testing Terms

by Glenn M. Duffield, President, HydroSOLVE, Inc.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Anisotropy: A physical property (e.g., hydraulic conductivity) which differs in magnitude according to direction.
Aquiclude: A water-bearing layer of rock or sediment that is incapable of transmitting water.
Aquifer: A water-bearing layer of rock or sediment capable of transmitting significant quantities of water.
Aquifer Diffusivity: See hydraulic diffusivity.
Aquifer Thickness (b): Saturated thickness of an aquifer. [L]
Aquifuge: See aquiclude.
Aquitard: A water-bearing layer of rock or sediment that transmits small quantities of water in relation to aquifers.
Artesian Aquifer: A confined aquifer in which the water level in wells rises above the top of the aquifer.

Coefficient of Hydraulic Conductivity: See hydraulic conductivity.
Coefficient of Storage: See storativity.
Coefficient of Transmissivity: See transmissivity.
Confined Aquifer: An aquifer confined between aquitards or aquicludes. See also leaky confined aquifer and nonleaky confined aquifer.
Confining Bed: See aquiclude and aquitard.
Confining Unit: See aquiclude and aquitard.
Constant-Head Boundary: An aquifer boundary where no drawdown occurs.

Darcy Velocity: See specific discharge.
Displacement (H): Change in water level (rise or fall) measured from static position. [L]
Drawdown: Change in water level due to an external stress such as pumping. [L]

Filter Pack: Material (typically sand or gravel) emplaced in well annulus around open interval of a well (e.g., well screen).
Flowing Artesian Aquifer: A confined aquifer in which the water level in wells rises above ground surface.
Full Penetration: A fully penetrating well has a perforated interval or screen extending over the full saturated thickness of an aquifer.

Hydraulic Conductivity (K): Constant of proportionality defining the specific discharge of a porous medium under a unit hydraulic gradient, $K = q / i$ . [L/T]

Hydraulic Diffusivity (α): The ratio of transmissivity to storativity, $α = T / S$ . [L²/T]
Hydraulic Gradient (i): Hydraulic head loss per distance, $i = d h / d l$ . [dimensionless]

Initial Displacement (H₀): Change in water level (rise or fall) measured from static position in the control well at start of a slug test. [L]
Interference Test: A pumping test performed with water levels recorded at one or more observation wells.

Leakance Coefficient: Vertical hydraulic conductivity of an aquitard divided by its thickness, $K' / b'$ . [1/T]
Leaky Confined Aquifer: A confined aquifer which has aquitards at its upper and/or lower boundaries.
Line Sink: A well represented mathematically as having an infinitesimally small radius.
Line Source: See line sink.

Negative Boundary: See no-flow boundary.
No-Flow Boundary: An aquifer boundary across which no flow occurs.
Nonleaky Confined Aquifer: A confined aquifer which has aquicludes at its upper and lower boundaries.

Nonsteady Flow: See transient flow.
Normalized Head (H/H₀): Displacement in a well divided by initial displacement. [dimensionless]

Partial Penetration: A partially penetrating well has a perforated interval or screen extending over a portion of the saturated thickness of an aquifer.

Phreatic Aquifer: See unconfined aquifer.
Porosity (n): Ratio of void volume ( $V_{v}$ ) to total volume ( $V_{t}$ ) in a rock or unconsolidated material, $n = V_{v} / V_{t}$ . [dimensionless]
Positive Boundary: See constant-head boundary.
Pumping Test: A field experiment in which a well is pumped at a controlled rate and water levels are recorded in nearby observation wells for the purpose of estimating aquifer properties (e.g., transmissivity and storativity).

Recharge Boundary: See constant-head boundary.
Residual Drawdown: Drawdown during the recovery phase of a pumping test after pumping stops. [L]

Sand Pack: See filter pack.
Specific Discharge (q): Flow rate per unit cross-sectional area of aquifer, $q = Q / A$ . Also known as Darcy velocity or Darcy flux given by the product of hydraulic conductivity and hydraulic gradient, $q = K i$ . [L/T]
Specific Storage (S_s): Volume of water released from storage from a unit volume of aquifer per unit decline in hydraulic head. [1/L]
Specific Yield (S_y): Volume of water released from storage by an unconfined aquifer per unit surface area of aquifer per unit decline of the water table. [dimensionless]

Storativity (S): Volume of water released from storage by a confined aquifer per unit surface area of aquifer per unit decline in hydraulic head normal to surface equal to product of specific storage and saturated thickness, $S = S_{s} b$ . [dimensionless]

Transient Flow: A flow field in which the flow velocity at any given point changes with time.
Transmissivity (T): The product of hydraulic conductivity and saturated thickness, $T = K b$ . [L²/T]

Unconfined Aquifer: An aquifer which has a water table forming its upper boundary.

Water Table: The surface in a porous medium on which fluid pressure is equal to atmospheric pressure.
Water-Table Aquifer: See unconfined aquifer.